Method and apparatus for extended life journal assembly

ABSTRACT

A method of extending the life of a journal bearing assembly in a solid fuel pulverizer includes: removing a first lower journal bearing from a journal shaft and a lower bearing seat of a lower bearing housing; removing a first upper journal bearing from the shaft and an upper bearing seat of an upper bearing housing; modifying the lower and upper bearing seats; modifying lower and upper shoulders on the journal shaft; disposing the second lower and upper journal bearings on the modified lower and upper bearing seats; disposing a new journal bearing spacer between the second lower and upper journal bearings; disposing a new journal bearing collar between the upper shoulder and the second upper journal bearing; filling a cavity defined by the lower and upper journal housings with grease; and disposing a seal assembly between the shaft and one end of the upper journal housing opposite the lower journal housing to prevent the ingress of solid fuel into the cavity of the journal assembly.

TECHNICAL FIELD

The present invention relates to a journal assembly for pulverizing asolid fuel, and more particularly, to an improved journal assembly whichaccommodates larger capacity tapered roller bearings while maintainingan existing journal assembly envelope for a mill for pulverizing a solidfuel, such as coal, for example, in a new utility unit application or aretrofit application in an existing utility unit.

BACKGROUND

Pulverizers are well known for the reduction of the particle size ofsolid fuel to allow for combustion of the solid fuel in a furnace. Apulverizer employs some combination of impact, attrition and crushing toreduce a solid fuel to a particular particle size. Several types ofpulverizer mills can be employed for the pulverization of the solidfuel, for example, coal, to a particulate size appropriate for firing ina furnace. These can include ball-tube mills, impact mills, attritionmills, ball race mills, and ring roll or bowl mills. Most typically,however, bowl mills with integral classification equipment are employedfor the pulverization of the solid fuel to allow for transport, dryingand direct firing of the pulverized fuel entrained in an air stream.

Bowl mills have a grinding ring carried by a rotating bowl. Fixedposition rollers are mounted on roller journal assemblies such that theroll face of the rollers are approximately parallel to the insidesurface of the grinding ring and define a very small gap therebetween.Pressure for grinding is applied through springs or hydraulic cylinderson the roller journal to crush solid fuel caught between the roll faceof the roller and the grinding ring.

An air stream is typically utilized for drying, classification, andtransport of the solid fuel through the pulverizer. The air streamemployed is typically a portion of the combustion air referred to as theprimary air. The primary air is combustion air first directed through apreheater whereby the combustion air is heated with energy recoveredfrom the flue gas of the furnace. A portion of the primary air is thenducted to the pulverizers. In a bowl mill, the primary air is drawnthrough beneath the bowl of the bowl mill and up past the roller journalassemblies to collect the pulverized solid fuel. The small particles ofsolid fuel become entrained in the primary air. The air streamcontaining the solid fuel then passes through a classifier into theoutlet of the pulverizer. After passing through the exhauster, thepulverized fuel can be stored, or more typically, is transported to thefurnace by the air stream for direct firing.

The journal loading, which dictates the amount of grinding force thatthe grinding rolls exert on the coal, to crush solid fuel caught betweenthe roll face of the roller and the grinding ring, has been provided todate either through the use of hydraulic systems or through the use ofmechanical springs. One such arrangement of mechanical springs can befound depicted, for example, in U.S. Pat. No. 4,706,900 entitled“Retrofitable Coiled Spring System,” which issued on Nov. 17, 1987 andwhich is assigned to the same assignee as the present invention. Inaccord with a showing contained in this U.S. patent, each grinding rollis urged towards the surface of the grinding table by means of anadjustable spring and is rotated about a fixed shaft within the journalassembly and connected to the rotatable grinding roll. To this end,journal bearings allow rotation of the journal assembly relative to theshaft and a spring capable of urging the grinding roll toward thegrinding table surface. The spring exerts a predetermined grinding forceon the coal disposed on the table when the coal is of a predetermineddepth on the table.

Although the journal bearings used in mill of U.S. Pat. No. 4,706,900have demonstrated to be operative for the purpose for which they havebeen designed, a need still exists to improve the mill loading and rolllife of the bearings. More specifically, the original roll life goal forthe journal bearings was 50,000 hours which translated into a roll lifeof only one or two years using Ni-Hard. However, today mill loading androll life demand has increased, with projections/demand extending to 82months (6.8 years) in some instances. Thus, there is a need for longerbearing lives across older, as well as newer, mill lines.

Another factor which deteriorates roll life of the bearings in additionto increased mill loading includes solid fuel dust, such as coal dust,for example, which flows into the journal assembly and contaminates thebearings and lubricant therefor. An interface between the rotatablejournal assembly and stationary shaft is exposed to atmosphericconditions and a differential pressure across the journal assemblyallows the coal dust, for example, to flow into the journal assemblyhousing the bearings. The ingress of coal at this interface, whichallows the shaft to extend therethrough and rotate with respect to thejournal assembly, contaminates the lubricant and journal bearings thusdeteriorating the roll life of the journal bearings.

Therefore, there remains a need for a method and apparatus forincreasing bearing roll life in a journal assembly, which facilitatesincreased mill loading and prevents contamination of the bearings, whileusing as much of the existing journal assembly envelope to reduce costs.

SUMMARY

According to the aspects illustrated herein, there is provided a methodof extending the life of a journal bearing assembly in a solid fuelpulverizer. The method includes: removing a first lower journal bearingfrom a journal shaft and a lower bearing seat of a lower bearing housingconfigured to support a grinding roll in the pulverizer; removing afirst upper journal bearing from the shaft and an upper bearing seat ofan upper bearing housing configured to be coupled to the lower bearinghousing; modifying the lower and upper bearing seats to provide modifiedlower and upper bearing seats; modifying bearing seats in lower andupper bearing housings defining the journal assembly to receive thelarger capacity lower and upper journal bearings; modifying lower andupper shoulders on the journal shaft to receive the larger capacitysecond lower and upper journal bearings, respectively, while retainingan original diameter of the journal shaft under the second largercapacity lower and upper journal bearings; disposing the second lowerand upper journal bearings on the modified lower and upper bearingseats, the second lower and upper journal bearings having at least oneof an increased diameter and width than the first lower and upperjournal bearings; disposing a new journal bearing spacer between thesecond lower and upper journal bearings; disposing a new journal bearingcollar between the upper shoulder and the second upper journal bearing;filling a cavity defined by the lower and upper journal housings withgrease; and disposing a seal assembly between the shaft and one end ofthe upper journal housing opposite the lower journal housing to preventthe ingress of solid fuel into the cavity of the journal assembly.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments, andwherein the like elements are numbered alike:

FIG. 1 is a side elevational view partially in section of a pulverizerbowl mill equipped with a journal assembly constructed in accordancewith the prior art;

FIG. 2 is an enlarged cross-sectional view of the journal assembly ofthe pulverizer bowl mill of FIG. 1 constructed in accordance with theprior art;

FIG. 3 is a cross-sectional view of a journal assembly accommodatinglarger capacity bearings in accordance with an exemplary embodiment ofthe present invention;

FIG. 4 is an enlarged cross-sectional view of the journal assembly ofFIG. 3 with a seal assembly and the bearings removed;

FIG. 5 is an enlarged partial cross-sectional view of detail ‘A’ in FIG.3 illustrating an exemplary embodiment of a seal between a shaft andupper journal housing of the exemplary journal assembly in accordancewith the present invention; and

FIG. 6 is an enlarged partial cross-sectional view of detail ‘B’ in FIG.5.

DETAILED DESCRIPTION

Referring now to the drawings, and more particularly to FIG. 1, apulverizing bowl mill 10 constructed in accordance with the prior art isillustrated. As the nature of the construction and the mode of operationof pulverizing bowl mills are well-known to those skilled in the art, itis not deemed necessary, therefore, to set forth herein a detaileddescription of the pulverizing bowl mill 10 illustrated in FIG. 1 of thedrawing. Rather, it is deemed sufficient for purposes of obtaining anunderstanding of a pulverizing bowl mill 10, which is equipped with ajournal assembly constructed in accordance with the present invention,that merely a description of the nature of the construction and the modeof operation of the components of the pulverizing bowl mill 10 withwhich the journal assembly cooperates. For a more detailed descriptionof the nature of the construction and the mode of operation of thecomponents of the pulverizing bowl mill 10, which are not described indetail herein, reference is made to the prior art, e.g., U.S. Pat. No.3,465,971, which issued on Sep. 9, 1969 to J. F. Dalenberg et al.,and/or U.S. Pat. No. 4,002,299, which issued on Jan. 11, 1977 to C. J.Skalka.

Still referring to FIG. 1, the pulverizing bowl mill 10 includes asubstantially closed separator body 12. A grinding table 14 is mountedon a shaft 16, which in turn is operatively connected to a suitabledrive mechanism (not shown) so as to be capable of being suitably driventhereby. With the aforesaid components arranged within the separatorbody 12 in the manner depicted in FIG. 1 of the drawing, the grindingtable 14 is designed to be driven in a clockwise direction.

A plurality of grinding rolls 18, preferably three in number in accordwith conventional practice, are suitably supported within the interiorof the separator body 12 so as to be equidistantly spaced one fromanother around the circumference of the separator body 12. In theinterest of maintaining clarity of illustration in the drawing, only onegrinding roll 18 is shown in FIG. 1. Each of the grinding rolls 18 issupported on a suitable shaft (not shown) of a journal assembly 19 forrotation relative thereto. The grinding rolls 18 are each suitablysupported in a manner for movement relative to the upper surface, asviewed with reference to FIG. 1, of the grinding table 14. To this end,each of the grinding rolls 18 has a biasing system 20, e.g., amechanical coiled spring system 20, cooperatively associated therewithvia the journal assembly 19. Each of the mechanical coiled springsystems 20 is operative to establish a mechanical spring loading on thecorresponding grinding roll 18 to exert the requisite degree of force onthe solid fuel disposed on the grinding table 14 for the desired purposeof pulverizing the solid fuel.

The solid fuel material, e.g., coal, which is pulverized in the bowlmill 10 is fed thereto through the use of any suitable conventional typeof feeding means such as a belt feeder (not shown). Upon falling free ofthe belt feeder (not shown), the coal enters the bowl mill 10 from acoal supply means, generally designated by reference numeral 22. Thecoal supply means 22 includes a suitably dimensioned duct 24 having oneend thereof which extends outwardly of the separator body 12 andpreferably terminates in a funnel-like member (not shown). The latterfunnel-like member (not shown) is shaped to facilitate the collection ofthe coal particles leaving the belt feeder (not shown), and to guide thecoal particles into the duct 24. The other end 26 of the duct 24 of thecoal supply means 22 is operative to effect the discharge of the coalonto the surface of the grinding table 14. As shown in FIG. 1, the ductend 26 is supported within the separator body 12 such that the duct end26 is coaxially aligned with the shaft 16, and is located in spacedrelation to an outlet 28 provided in a classifier 30, through which thecoal flows in the course of being fed onto the surface of the grindingtable 14.

A gas such as air is used to convey the finer ground coal from thegrinding table 14 through the interior of the separator body 12 fordischarge from the pulverizing bowl mill 10. The air enters theseparator body 12 through a suitable opening (not shown) providedtherein for this purpose. The air flows to a plurality of annular spaces32 from the aforesaid opening (not shown) in the separator body 12. Theplurality of annular spaces 32 are formed between the circumference ofthe grinding table 14 and the inner wall surface of the separator body12. The air upon exiting from the annular spaces 32 is deflected overthe grinding table 14 by means of suitably positioned deflector means(not shown). One such form of deflector means (not shown), which issuitable for this purpose in the bowl mill 10 of FIG. 1, comprises thesubject matter of U.S. Pat. No. 4,234,132, which issued on Nov. 18, 1980to T. V. Maliszewski, Jr., and which is assigned to the same assignee asthe present application.

While the air is flowing along the path described above, the coaldisposed on the surface of the grinding table 14 is pulverized by thegrinding rolls 18. As the coal becomes pulverized, the particles arethrown outwardly by centrifugal force away from the center of thegrinding table 14. Upon reaching the peripheral circumferential area ofthe grinding table 14, the coal particles are picked up by the airexiting from the annular spaces 32 and are carried along therewith. Thecombined flow of air and coal particles is thereafter captured by thedeflector means (not shown). The deflector means causes the combinedflow of air and coal particles to be deflected over the grinding table14. In the course of effecting a change in direction in the path of flowof this combined stream of air and coal particles to be deflected overthe grinding table 14, the heaviest coal particles, because they havemore inertia, become separated from the airstream and fall back onto thegrinding table 14 whereupon they undergo further pulverization. Thelighter coal particles, on the other hand, because they have lessinertia continue to be carried along in the airstream.

After leaving the influence of the aforesaid deflector means (not shown)the combined stream of air and remaining coal particles flow to theclassifier 30. The classifier 30, in accord with conventional practiceand well-known to those skilled in the art, further sorts the coalparticles that remain in the airstream. Namely, those particles ofpulverized coal, which are of the desired particle size, pass throughthe classifier 30 and along with the air are discharged from the bowlmill 10 through the outlets 34. However, the coal particles having asize larger than desired are returned to the surface of the grindingtable 14 whereupon they undergo further pulverization. Thereafter, thesecoal particles are subject to repetition of the process described above.That is, the particles are thrown radially outwardly of the grindingtable 14, are picked up by the air exiting from the annular spaces 32,are carried along with the air to the deflector means (not shown), aredeflected back over the grinding table 14 by the deflector means (notshown), the heavier particles drop back on the grinding table 14, thelighter particles are carried along to the classifier 30, thoseparticles which are of the proper size pass through the classifier 30and exit from the bowl mill 10 through the outlets 34.

The amount of force that must be exerted by the grinding rolls 18 inorder to effect the desired degree of pulverization of the coal willvary depending on a number of factors. In other words, the amount offorce that the grinding rolls 18 must exert in order to accomplish thedesired pulverization of the coal is principally a function of theamount, e.g., depth, of coal present on the grinding table 14. In turn,the amount of coal which is disposed on the grinding table 14 is afunction of the output rate at which the bowl mill 10 is being operatedto produce pulverized coal.

The amount of grinding force which the grinding rolls 18 apply to thecoal on the grinding table 14 is a function of the amount of force withwhich the grinding rolls 18 are biased into engagement with the coal onthe table 14 via the biasing system 20. The grinding roll 18 issupported so as to be pivotable about a pivot pin 36 into and out ofengagement with the coal disposed on the grinding table 14. Althoughonly one grinding roll 18 is shown in FIG. 1 and although thisdiscussion is directed to one grinding roll 18, it is to be understoodthat the bowl mill 10 commonly is provided with a plurality of grindingrolls 18, e.g., preferably three in number, and that this discussion isequally applicable to each of the plurality of grinding rolls 18.

The grinding roll 18 is designed to be biased by a force into and out ofengagement with the coal on the grinding table 14. More specifically,the force applied to the grinding roll 18 is a spring force applied bythe mechanical coiled spring system 20, which produces an axial forceapplied to the grinding roll 18.

FIG. 2 illustrates an enlarged cross-sectional view of the journalassembly 19 removed from the pulverizer bowl mill 10 of FIG. 1constructed in accordance with the prior art. The journal assembly 19includes grinding roll 18 coupled to a lower journal housing 100, whichin turn is coupled to an upper journal housing 102. The lower and upperjournal housings 100, 102 receive a shaft 104 therethrough via a lowerjournal bearing 106 and an upper journal bearing 108 disposed at thelower and upper journal housings 100, 102, respectively. An upperjournal housing cover 110 covers mounting flanges of the respectivelower and upper journal housings 100, 102. A bearing spacer 112 spacesthe lower and upper journal bearings 106, 108 apart from one another ina bath of oil (not shown) to lubricate the journal bearings 106, 108housed in the lower and upper journal housings 100, 102, respectively.However, as discussed above, there is a desire to increase the roll lifeof the journal bearings and prevent ingress of coal contamination intothe oil lubricant and journal bearings.

To this end, the bowl mill 10 embodies a plurality of new and improvedjournal assemblies 190, as partially illustrated in FIGS. 3 and 4. Thatis, in accord with the best mode embodiment of the present inventioneach of the three grinding rolls 18 with which the bowl mill 10 isprovided has cooperatively associated therewith a new and improvedjournal assembly 190. However, inasmuch as the three journal assemblies190 are each identical in construction and in mode of operation, it hasbeen deemed sufficient for purposes of obtaining an understandingthereof as well as in the interest of maintaining clarity ofillustration in the drawing to show only one of the three journalassemblies 190 in FIGS. 3 and 4.

Turning now to consideration in further detail of the nature of theconstruction of the exemplary journal assembly 190, general referencewill be made first to FIG. 3 for this purpose in describing the journalassembly 190. As depicted therein, the journal assembly 190, akin to thejournal assembly 19 of FIG. 2, includes the following major components:a grinding roll 180 coupled to a lower journal housing 200, which inturn is coupled to an upper journal housing 202. The lower and upperjournal housings 200, 202 receive a shaft 204 therethrough via a lowerjournal bearing 206 and an upper journal bearing 208 disposed at thelower and upper journal housings 200, 202, respectively. An upperjournal housing cover 210 covers mounting flanges 214, 216 of therespective lower and upper journal housings 200, 202. A bearing spacer212 spaces the lower and upper journal bearings 206, 208 apart from oneanother housed in a cavity 218 defined by the lower and upper journalhousings 200, 202, respectively. In addition, the journal assembly 190includes a seal assembly 220 disposed at an interface between the upperjournal housing 202 and the shaft 204. The seal assembly 220 preventsingress of solid fuel, e.g., coal, into the cavity 218, thus preventingcontamination of the journal bearings 206, 208 and grease lubricanttherefor (not shown) in the cavity 218.

Still referring to FIG. 3, the journal assembly 190 will be discussed inmore detail. In order to increase the roll life of the journal bearings206, 208 in journal assembly 190 over that of the journal bearings 106,108 in the conventional journal assembly 19 of FIG. 2, bearings 206, 208are larger capacity tapered roller bearings 206, 208 than bearings 106,108. For example, the original upper journal bearing 108 employed in thejournal assembly 19 of FIG. 2 may be configured as follows, but notlimited thereto: Bore=5.0000 inches, outside diameter (OD)=8.5000inches, Width=1.875 inches, Dynamic Radial Capacity=20,600 lbs., DynamicThrust Capacity=17,200 lbs. The original lower journal bearing 106employed in the journal assembly 19 may be configured as follows, butnot limited thereto: Bore=4.5000 inches, OD=8.3750 inches, Width=2.6250inches, Dynamic Radial Capacity=36,700 lbs., Dynamic ThrustCapacity=20,500 lbs. In contrast, the new upper journal bearing 208employed in the journal assembly 190 of FIG. 3 may be configured asfollows, but not limited thereto: Bore=5.0000 inches, OD=9.0000 inches,Width=2.1250 inches, Dynamic Radial Capacity=26,700 lbs., Dynamic ThrustCapacity=33,700 lbs. Likewise, the new lower journal bearing 206employed in the journal assembly 190 may be configured, as follows, butnot limited thereto: Bore=4.5000 inches, OD=9.5000 inches, Width=3.5000inches, Dynamic Radial Capacity=50,400 lbs., Dynamic ThrustCapacity=36,200 lbs. The above information is represented in Table 1below:

TABLE 1 Dynamic Dynamic Radial Thrust Bore OD Width Capacity Capacity(inches) (inches) (inches) (pounds) (pounds) Original 5.0000 in. 8.5000in.  1.875 in. 20,600 lbs. 17,200 lbs. Upper Bearing 108 New 5.0000 in.9.0000 in. 2.1250 in. 26,700 lbs. 33,700 lbs. Upper Bearing 208 Original4.5000 in. 8.3750 in. 2.6250 in. 36,700 lbs. 20,500 lbs. Lower Bearing106 New 4.5000 in. 9.5000 in. 3.5000 in. 50,400 lbs. 36,200 lbs. LowerBearing 206

Therefore, a ratio of new/original Dynamic Radial Capacities shows acalculated increase in L10 bearing life of over 2.5 times. Thus,reference to larger “capacity” with respect to journal bearings 206 and208 means the increased dynamic radial capacity which translates into anincreased L10 bearing life over the original journal bearings 106 and108. In particular, the dynamic radial capacity increases at least 25%for both the new upper and lower tapered roller bearings 206, 208. Inexemplary embodiments and from Table 1 above, it can been seen that thedynamic radial capacity of the upper tapered roller bearing 208increases about 29.61%, while the dynamic radial capacity of the lowertapered roller bearing 206 increases about 37.33%. The larger capacitytapered roller bearings 206, 208 are also lubricated with grease insteadof oil and the seal assembly 220 prevents contamination of the greaselubricant and journal assembly tapered roller bearings 206, 208.Furthermore, the use of the seal assembly 220 allowing the use ofgrease, rather than oil, to lubricate the bearings 206, 208 has alsobeen discovered to increase bearing life.

However, with the goal of using larger capacity tapered roller bearings206, 208 to increase roll life between journal assembly rebuilds, it isalso desired to maintain an existing journal assembly envelope. In orderto accommodate larger capacity tapered roller bearings 206, 208 in theexemplary journal assembly 190 without changing the outside boundarydimensions thereof, it will be recognized by those skilled in thepertinent art that respective bearing seats 207, 209 (FIG. 4) of thelower and upper journal housings 200, 202, as well as the shaft 204, aremodified to accommodate the increased outside diameter and width(elevation height as illustrated) of the larger capacity tapered rollerbearings 206, 208. Because of the wider roller bearings 206, 208, thebearing spacer 212 is a new part, which replaces the bearing spacer 112in FIG. 2. In addition, a new journal bearing collar 222 is incorporatedhaving dimensions corresponding to the new bearing width of bearing 208.

Since the bearings 206, 208 in FIG. 3 are wider than bearings 106, 108in FIG. 2, the shaft 204 is modified to locate shoulders 229, 231 (FIG.4) thereof corresponding to abutment with inner races of the respectivebearings 206, 208. However, a bore diameter of the inner races for eachof the tapered roller bearings 206, 208 are selected or designed so thatchanges to a corresponding diameter 233, 235 (FIG. 4) of the shaft 204under each bearing 206, 208 are not necessary as illustrated withreference to Table 1 above. In particular, a wider lower bearing seat(illustrated as an increased elevation height in FIG. 4 and opposite thelower bearing seat 207 of the lower journal housing 200) to accommodatethe wider, lower journal bearing 206 is reflected by the shoulder 229 ina lower portion of the shaft 204, while retaining a same diameter of theshaft 204.

In addition, the new or modified shaft 204 includes a seal land with anappropriate finish for the seal assembly 220, discussed more fully belowwith respect to FIGS. 5 and 6. Therefore, minimal change to the shaft204 is required to accommodate the larger capacity tapered rollerbearings 206, 208.

Incorporation of the larger lower tapered roller bearing 206 in the newor modified lower journal housing 200 includes the lower bearing cupseat 207 corresponding to an outer race 224 of the lower bearing 206 toreceive the outer race 224 of the lower bearing 206. The lower bearingcup seat 207 is larger in diameter than in the conventional lowerjournal housing 100. The lower journal housing 200 also includes ahousing bore diameter larger than the upper journal housing OD 202 atthe diameter generally indicated at 225 of the upper journal housing202. The upper journal housing OD 202 is configured for installationwith an O-ring oil seal 227 disposed between the two diameters 225 andthus between the lower and upper journal housings 200, 202.

Likewise, incorporation of a larger upper tapered roller bearing 208 inthe new or modified upper journal housing 202 includes the upper bearingcup seat 209 at one end of the upper journal housing 202 that is bothwider and larger in diameter than in the conventional upper journalhousing 102. A counter bore 226 and a snap ring groove 228 areconfigured at an opposite end of the new or modified upper journalhousing 202 to receive a snap ring 230 and the seal assembly 220, asbest seen with reference to FIG. 6 and discussed more fully below.

Referring now to FIGS. 5 and 6, FIG. 6 is an enlarged partialcross-sectional view of detail ‘A’ in FIG. 3 illustrating an exemplaryembodiment of the seal assembly 220 between the shaft 204 and upperjournal housing 202 of the exemplary journal assembly 190 in accordancewith the present invention. FIG. 6 is an enlarged partialcross-sectional view of detail ‘B’ in FIG. 5. The seal assembly 220includes an oil seal 232 and a wear sleeve 234. The oil seal 232 isdisposed in the counterbore 226 and is in sealing communication with thewear sleeve 234 disposed around the shaft 204 aligned with thecounterbore 226 on the upper journal housing 202. More specifically, theoil seal 232 comprises a continuous outer ring 236 which abuts thecounterbore 226 and a plurality of members 238 extending radiallyinwardly from the outer ring 236 at an oblique angle from the ring 236for abutment with the wear sleeve 234. The seal 232 is flexible allowingrelative rotational motion of the upper journal housing 202 relative tothe stationary shaft 204, while maintaining a positive seal to preventthe ingress of coal. The snap ring 230 is disposed in the snap ringgroove 228 to retain the oil seal 232 in the counterbore 226.

Assembly of the journal shaft 204, bearings 206, 208 and upper and lowerjournal housings 202, 200 is substantially the same as for assembly ofthe conventional journal assembly 19 with a few differences. Thesedifferences primarily include installing the wear sleeve 234 on theshaft 204, packing the seal assembly 220 with grease and installing theseal 232 and retaining ring 230. In addition, as alluded to before, theshaft 204, housings 200, 202 (e.g., cavity 218), tapered roller bearing206, 208 are filled with grease as a lubricant during the assembly toensure the final grease fill.

Referring again to FIG. 3, the assembly of journal assembly is describedin further detail below. The wear sleeve 234 is heated in an oil bath toa temperature of 250° F. The wear sleeve 234 is a cylindrical hollowsleeve that is then slid into position on the journal shaft 204 andallowed to cool. A shaft bore 240 defined by the shaft 204 is filledwith grease prior to installing a pipe plug 242 to seal the shaft bore240.

The bearing voids of bearings 206, 208 are also packed with greasebefore final assembly. The lower journal housing 200 defining the cavity218 is filled approximately ⅔ full of grease. Then the seal 232 isinstalled into the counterbore 226 of the upper journal housing 202. Theremaining cavity 218 defined by the upper journal housing 202 is filledwith grease before installing the retaining ring 230 in the groove 228of the upper journal housing 202.

After the lower journal bearing 206 is installed with the shaft 204, aroller bearing keeper 244 and lock plate 246 are fastened to a bottom ofthe shaft 204 using mechanical fasteners 248, such as threaded bolts,for example, but is not limited thereto. A journal bearing shim 250 maybe used to properly space the lower journal bearing 206 and keeper 244.

The lower portion of the shaft 204, as illustrated in FIG. 3, is slowlylowered into the lower journal housing. Then the remaining ⅓ of thecavity 218 defined by the lower journal housing 200 is filled withgrease. The upper journal housing 202 can then be assembled to the lowerjournal housing 200 and fastened together using mechanical fasteners252, such as threaded bolts, for example, but is not limited thereto.

It should be noted that due to the hardness of the grinding roll 180 inexemplary embodiments, the grinding roll 180 is spot drilled through setscrew holes in a locknut 254 prior to installing set screws 256 in theset screw holes. It should also be noted that this final assembly uses astandard lock tab application 260 as in the conventional journalassembly 19 in FIG. 2.

The journal assembly 190 of FIGS. 3 and 4, in accordance with exemplaryembodiments of the present invention, allows for larger capacity upperand lower journal bearings which provide longer grinding roll life andrequire fewer journal rebuilds over a same period of time. Use of thelarger capacity upper and lower journal bearings provide lower bearingloads and contact stresses, and thus longer bearing service liveshelping to ensure fewer journal rebuilds. The longer bearing servicelives and fewer journal rebuilds facilitates attainment of the roll lifegoal extending to 82 months. The larger capacity upper and lower journalbearings incorporate the use of new or modified assembly componentsdiscussed above while retaining an original envelope. Customers canchoose between newly manufactured shaft and journal housing componentsor remanufactured components with the above exemplary embodiments.Lastly, the seal assembly disposed at one terminal end of the upperjournal housing incorporates proven seal technology and prevents theingress of coal and contamination of the grease lubricant and journalassembly tapered roller bearings. In this manner, the seal assemblyeffectively prevents solid fuel dust, such as coal dust, for example,from penetrating into the journal assembly cavity. Lastly, exemplaryembodiments of the journal assembly in accordance with the presentinvention permit the larger capacity tapered roller bearings of FIG. 3to be retrofitted into the journal assembly of FIG. 2 while maintainingas many original parts as possible.

While the invention has been described with reference to variousexemplary embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method of extending the life of a journal bearing assembly in asolid fuel pulverizer, the method comprising: removing a first lowerjournal bearing from a journal shaft and a lower bearing seat of a lowerbearing housing configured to support a grinding roll in the pulverizer;removing a first upper journal bearing from the shaft and an upperbearing seat of an upper bearing housing configured to be coupled to thelower bearing housing; modifying the lower and upper bearing seats toprovide modified lower and upper bearing seats; modifying lower andupper shoulders on the journal shaft to receive second lower and upperjournal bearings, respectively, while retaining an original diameter ofthe journal shaft under the second lower and upper journal bearings;disposing the second lower and upper journal bearings on the modifiedlower and upper bearing seats, the second lower and upper journalbearings having at least one of an increased diameter and width than thefirst lower and upper journal bearings; disposing a new journal bearingspacer between the second lower and upper journal bearings; disposing anew journal bearing collar between the upper shoulder and the secondupper journal bearing; filling a cavity defined by the lower and upperjournal housings with grease; and disposing a seal assembly between theshaft and one end of the upper journal housing opposite the lowerjournal housing to prevent the ingress of solid fuel into the cavity ofthe journal assembly.
 2. The method of claim 1, wherein the sealassembly further comprises a wear sleeve disposed around the journalshaft and sealably engaged with an oil seal disposed in a counterbore ofthe upper journal housing.
 3. The method of claim 2, wherein the sealassembly further comprises a retaining ring disposed in a groove in theupper journal housing to retain the oil seal in the counterbore.
 4. Themethod of claim 2, further comprising: heating the wear sleeve in an oilbath to a temperature of 250° F.; disposing the wear sleeve over theshaft; and allowing the wear sleeve to cool to be fixedly attached tothe shaft at a position corresponding to the oil seal.
 5. The method ofclaim 2, wherein the seal is flexible allowing rotational motion of theupper journal housing relative to the stationary shaft, whilemaintaining a positive seal.
 6. The method of claim 2, wherein the lowerand upper shoulders of the shaft are modified corresponding to amodified width of the second lower and upper journal bearings.
 7. Themethod of claim 1, wherein the second lower and upper journal bearingsare larger tapered roller journal bearings each providing at least a 25%increase in dynamic radial capacity over the first lower and upperjournal bearings.
 8. The method of claim 1, wherein the lower and upperhousings are new or modified existing lower and upper journal housings.9. The method of claim 1, wherein the journal shaft is a new or modifiedexisting journal shaft.
 10. The method of claim 1, wherein the solidfuel is coal.
 11. The method of claim 1, wherein modifying the lower andupper bearing seats includes increasing at least one of a diameter and awidth of the lower and upper bearing seats corresponding to at least oneof the increased diameter and width of the second lower and upperjournal bearings.